• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.94-101
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• 2013

The market for NAND flash-based storage devices has grown significantly as they rapidly replace traditional disk-based storage devices. Heterogeneous NAND flash-based storage devices using both multi-level cell (MLC) and single-level cell (SLC) NAND flash memories are also actively researched since both types of memories complement each other. Heterogeneous NAND flash-based storage devices suffer from the overheads incurred by migration from SLC to MLC and garbage collection of SLC. This paper proposes a new flash translation layer (FTL) for heterogeneous NAND flash-based storage devices to reduce the overheads by utilizing SLC efficiently. The proposed FTL analyzes the access patterns of logical blocks and selects and stores only logical blocks expected to bring performance improvement in SLC. The experimental results show that the total execution time of heterogeneous NAND flash-based storage devices with our proposed FTL scheme is 35% shorter than that with the previously proposed best FTL scheme.

• Journal of Advanced Navigation Technology
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• v.12 no.5
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• pp.437-443
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• 2008

In this paper, we derive the optimum number of users which can maximize the information theoretic sum capacity in multiuser OFDM virtual MIMO uplink system. In which, there are multiple antennas at the base station and a number of users with single transmit antenna. Pilot-assisted channel state estimation is assumed for a block fading channel and time-varying fading channel. We analyze the tradeoff between the multiplexing gain and pilot overhead especially in low SNR regime and conclude that the optimum number of users is min ($N_r$,LT/2 ) in frequency nonselective block fading channel and approximately equal to min ($N_r$, ${\lfloor}{\sqrt{LT+1}}-1{\rfloor}$) in time varying fading channel. assuming the same pilot and signal pwoer.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.36C no.12
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• pp.47-58
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• 1999

As the performance of processors improves, cache memories are used to overcome the difference of speed between processors and main memories. Generally cache memories are embedded and small sizes, fault coverage is a more important factor than test time in testing point of view. A new test algorithm and a new BIST architecture are developed to detect various fault models with a relatively small overhead. The new concurrent BIST architecture uses the comparator of cache management blocks as response analyzers for tag memories. A modified scan-chain is used for pre-testing of comparators which can reduce test clock cycles. In addition several boundary scan instructions are provided to control the internal test circuitries. The results show that the new algorithm can detect SAFs, AFs, TFs linked with CFs, CFins, CFids, SCFs, CFdyns and DRFs models with O(12N), where N is the memory size and the new BIST architecture has lower overhead than traditional architecture by about 11%.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.11 s.353
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• pp.69-76
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• 2006

This paper proposes a self-repair system which is able to self-repair in cell unit by imitating the structure of living beings. Because the data of artificial cells move even diagonally, our system can self-repair faults not in column unit, but in cell unit. It leads to design an efficient self-repair system for multiple faults. Moreover, in artificial cell design, the usage of logic-based design method has smaller system size than that of the previous register-based design method. Our experimental result for 2-bit up/down counter shows 40.3% reduction in hardware overhead, compared to the previous method [6].

• Journal of IKEEE
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• v.23 no.4
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• pp.1343-1352
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• 2019

To manage the Internet of Things(IoT) Network, which consists of a large number of various devices, a secure and automatic method of strengthening the IoT network is being proposed. Blockchain has a 'smart contract' element of autonomous execution method, which is emerging as a way to not only exchange data quickly without mediators but also securely and automatically manage processes between IoT devices. In this paper, we implement a prototype of the entire IoT device management system based on the EOSIO with DPoS(Distributed Proof of Stake)-based blockchain structure, proposed as a prior study, including the user application DApp(Decentralized Application) and the actual IoT devices (Raspberry Pi-based device, and smart lamp) that interact with the blockchain platform. We analyze the benefits of the system and measure the time overhead to show the feasibility of the system.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.76-81
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• 2008

The vibration test system of satellite environment test dept. has been used successfully for the vibration tests of a majority of korean space programs. To meet the recent needs of large size test facility available for the vibrational tests of the huge launch vehicles and satellites, KARI have developed the large size multi-electromagnetic shaking system with $3{\times}3m$ head expander system. The new system will consist of three electromagnetic shakers which has 160 kN thrust force individually, and be able to sustain up to 8 tons test load and 300 kNm overturing moment. This paper describes the design components in the development process of multi-excitation shaker system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3553-3558
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• 2009

This study has been conducted to improve coolant flow pattern in the gasoline engine. Flow field has been calculated for the coolant passage mainly around the exhaust ports and valves. For the original model, a flow stagnant region has existed between exhaust valves of the second cylinder. To improve coolant flow characteristics, coolant passage area has been re-modeled and optimized. Furthermore, for the improved coolant core model, coolant passage under the exhaust manifold has been added to reduce exhaust-gas temperature. It was found that the flow through a gasket plays a critical role for the flow in the cylinder head and around exhaust valves. Finally, coolant flow around exhaust valves and in the cylinder head has been improved in terms of flow rate distribution.

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.1_2
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• pp.118-124
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• 2004

In this paper we propose a method for authenticating the application that is to be downloaded or updated in smart cards. Previous works have some drawbacks such as having a long verification delay or requiring a large amount of primary/secondary storage. We propose an efficient parameterized scheme by using the hash chain technique where the secondary storage requirement and verification delay of updating the application are O(k) and O(k＋n/k), respectively. Moreover, both the first storage requirement and verification delay of downloading the application are O(1).

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.5
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• pp.245-258
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• 2001

VLIW에서는 프로그램 코드를 병렬화 하는 작업이 모두 컴파일러에 의해서만 이루어진다. 따라서 병렬로 수행될 연산어들을 명시적으로 나타내 주어야 하며, 이를 위한 명령어 인코딩 방식으로 전개 인코딩 방식과 압축 인코딩 방식이 사용되어 왔다. 각 인코딩 방식들은 명령어의 적재 및 검색을 위해 서로 다른 캐쉬 구조를 필요로 하는데, 전개 인코딩 방식으로 비압축 캐쉬를 압축 인코딩 방식으로 압축 캐쉬를 사용하고 있다. 그러나 이들은 각각 무효 연산어로 인한 메모리 활용 효율 저하와 복원 과정으로 인한 명령어 인출 오버헤드의 증가라는 문제점을 안고 있다. 본 논문에서는 부분적으로 명령어 길이를 일정하게 유지하는 부분 압축 인코딩을 사용해 메모리 활용 효율을 높이는 동시에 명령어 인출 오버헤드를 줄일 수 있는 분할 캐쉬 구조를 제안한다. 각 캐쉬 구조를 구현하는데 필요한 칩 영역을 계산하여, 분할 캐쉬가 비교적 비용 효율적인 캐쉬 구조임을 확인하였다. 모의 실험을 통한 메모리 활용 효율 측정 결과 하드웨어 비용의 증가를 고려하더라도 분할 캐쉬는 비압축 캐쉬에 비해 최고 약 3배의 메모리 활용 효율을 얻을 수 있었다. 각 캐쉬 구조를 일차 캐쉬로 하는 VLIW 시스템들의 성능 측정 결과는 TCSC(블록 집중형 분할 캐쉬)를 사용한 시스템이 비용 대비 성능 면에서 가장 우수한 것으로 나타났다.

• The KIPS Transactions:PartB
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• v.8B no.1
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• pp.89-97
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• 2001

대용량 멀티미디어 미디어 서버를 구성함에 있어 I/O 병목현상을 극복하기 위하여 저장 서버들과 제어 서버로 구성되어진 2계층 분산 클러스터 서버구조가 많이 사용된다. 2 계층 분산 클러스터 서버는 부하 균등, 대역폭 관리 및 저장 서버의 관리 측면에서 유리한 반면, 저장 서버와 제어 서버간의 통신 오버헤드를 발생시킨다. 이러한 오버헤드를 줄이기 위해서는 저장 서버에서 읽은 미디어 데이터를 제어 서버를 거치지 않고 직접 클라이언트에 전송할 수 있어야 한다. 그리고, 저장 용량을 확장하거나 손상된 디스크를 교체하는 경우를 대비하여 분산 클러스터 서버는 다양한 성능의 이기종 디스크를 지원하여야 한다. 또한, I/O 장치와 운영체제가 빠르게 발전됨에 따라 미디어 서버는 새로운 I/O 장치 및 운영체제 등에 쉽게 이식될 수 있어야 하고, 응용 소프트웨어 개발자가 시스템의 환경에 따라 블록크기, 데이터 배치정책, 사본 정책 등을 유연하게 조절할 수 있어야 한다. 본 논문에서 위에서 언급한 멀티미디어 서버의 요구를 고려하여 Fast Ethernet 환경에서 병렬 멀티미디어 파일 시스템(PMFS : Parallel Multimedia File System)을 설계 및 구현하고 실험을 통해 PVFS(Parallel Virtual File System)와 성능을 비교 분석하였다. 이 실험의 결과에 따르면 PMFS는 멀티미디어 데이터에 대하여 PVFS보다 3%∼15%의 향상된 성능을 보였다.